In brief, solvent extraction columns are employed to achieve mass transfer between immiscible phases introduced into the column. For example, in the reprocessing of irradiated nuclear fuel, the fuel is dissolved in acid to provide an aqueous phase which is brought into contact with an appropriate solvent phase in the column to effect preferential extraction of uranium and plutonium from the aqueous phase into the solvent phase whilst leaving fission products in the aqueous phase. For effective operation it is required to ensure effective distribution of the phases in the column. The column, which can be pulsed, can be operated either in a solvent continuous or aqueous continuous mode.
In the solvent continuous mode, an aqueous feed is introduced into an upper region of the column to fall through the less dense solvent phase rising through the column. In the aqueous continuous mode, a solvent feed is introduced into a lower region of the column to rise through the denser aqueous phase filling through the column. As the inlet ports for the aqueous and solvent feeds are positioned in the wall of the column the incoming feed tends to remain in that region of the continuous phase which is adjacent the inlet over the length of the column. Consequently a large proportion of the continuous phase within the column is effectively unused for the mass transfer effect.
It is an aim of the invention to provide a solvent extraction column which is capable of distributing the feed over an increased extent of the column than hitherto.